To get the blue key, go west from the central octagonal room, down the lifts and along the corridor to the north. You will enter a room with some shotgun guys and a berserk to the south. Getting the berserk opens up a corridor to the north leading to a teleporter. This teleporter takes you to the blue key room. The switch in the south of this room opens up a door back to normal territory.

First get the blue key (see above). Now go through the blue door to the west and drop into the nukage. There is a secret door to the east (next ot the entrance to this room) leading to a stimpack and a radiation shielding suit. There is also a door to a room with a backpack, a megaarmor, and two switches. One opens a door to the south, the other reveals a switch in the room to the south, which raises the steps to the nearby BFG9000. (sector 121)